1. Field of the Invention
The present invention relates generally to structures for fixing screen bars of screening apparatuses which are installed in wastewater treatment plants to remove impurities from wastewater and, more particularly, to a structure for fixing screen bars of a screening apparatus for wastewater treatment in which the screen bars are provided at positions spaced apart from each other at predetermined intervals to have gaps ranging from 1 mm to 10 mm therebetween, and which is constructed such that, in a process of removing fine suspended solids from water, impurities such as hairs, which are relatively long, are prevented from being wound around support bars, which are perpendicularly provided under the screen bars to support the screen bars, thus preventing rakes from being undesirably flip or damaged by the wound impurities, and preventing gaps between the screen bars from being clogged with the impurities, thereby preventing the overflow of wastewater.
2. Description of the Related Art
As well known to those skilled in the art, screening apparatuses for wastewater treatment are classified into the coarse screening apparatus which screen bars are arranged to have gaps ranging from 50 mm to 100 mm to remove relatively large impurities for protecting machines disposed behind the screen, the fine screening apparatus which screen bars are arranged to have gaps ranging from 20 mm to 40 mm to remove smaller impurities, and the superfine screening apparatus which screen bars are arranged to have gaps ranging from 1 mm to 10 mm to remove fine suspended solids, which are the majority of suspended solids contained in wastewater, installed behind the coarse screening apparatus or behind the fine screening apparatus.
Such the screening apparatuses are consisted of a screen panel and some rake units. The screen panel is formed by arranging steel bars such as flat bars having rectangular cross-sections, round bars, or wedge bars having inverted triangular cross-sections, parallel to each other at predetermined intervals, and is installed in a wastewater flowing channel or a water tank and is oriented in a vertical direction or at a slight incline with respect to the vertical direction. The rake unit rakes and pulls the impurities up, which are caught by the screen bars but do not pass through gaps between the screen bars while wastewater flows through the screening apparatus, towards the upper end of the screen panel, and exhausts the impurities outside the screening apparatus.
In the case of the coarse screening apparatus or the fine screening apparatus, flat bars, each of which has a cross-section of 9 mm in thickness and 75 mm in width, are placed upright and are arranged parallel to each other at intervals ranging from 20 mm to 100 mm to fix the screen bars for filtering out impurities larger than the gaps while wastewater flows through the screening apparatus. Thereafter, holes are formed in the flat bars at positions that are spaced apart from each other at intervals ranging from 40 cm to 80 cm in the vertical direction. Subsequently, in a state in which spacing pipes, each of which has a length corresponding to the width of the gap, ranging from 20 mm to 100 mm are fitted between the screen bars. And round bars, each of which has a length corresponding to the entire width of the screen panel and has an external thread on the each end thereof, are inserted into the respective holes which are formed in the flat bars.
And in the case where round bars or wedge bars are used as screen bars, support bars which are made of flat bars or round bars, and have a length corresponding to the width of the screen panel are arranged at positions spaced apart from each other at intervals ranging from 40 cm to 50 cm. Thereafter, the round screen bars or wedge screen bars are placed on the support bars at intervals ranging from 20 mm to 40 mm parallel to each other such that are perpendicular to the support bars. And then, the round bars or wedge bars are fixed to the support bars by welding, thus forming the screen panel.
However, in the case of the superfine screen, having gaps ranging from 1 mm to 10 mm, the screen bars are easily bent as round bars or wedge bars used as the screen bars have diameters or cross-sectional widths ranging from 2 mm to 4 mm, which is very thin. Thus, to maintain the straightness of the screen bars and gaps between the screen bars constant, the intervals between support bars, which are arranged perpendicular to the screen bars and are welded to the rear surfaces of the screen bars, must be very short, typically ranging from 5 cm to 15 cm.
Furthermore, welding beads are formed on the surfaces of the support bars by the welding between the support bars and the screen bars, and the surfaces of the support bars are rough. Therefore, stringy impurities, such as hairs, strings, etc., contained in wastewater, which flows through the gaps between the screen bars, are easily entangled on at least several hundreds or thousands of welding portions between the support bars and the screen bars, and the amount of entangled impurities gradually increases. As a result, there is a problem in that the teeth of each rake, which are inserted into the respective gaps between the screen bars and move upwards along the screen bars, are interfered by the entangled impurities and are thus bent or damaged.
In an effort to overcome the above-mentioned problem experienced with the conventional technique, cushion hinge mounted rake devices using the tension of springs to overcome the problem of damage of the rakes were proposed in Korean Utility Model Registration No. 0104628 and No. 0129369. However, in the case where the amount of impurities entangled in the screen bars is gradually increased, and thus the cushion hinge mounted rakes repeatedly flip while moving along the screen bars, the springs for the cushion hinge mounted rakes may be broken.
Furthermore, because the drag force of the rakes is notably weakened by the elastic rotation of the springs, although the rakes repeatedly and continuously move along the screen bars and rake the gaps between the screen bars, impurities, which are entangled in the support bars, may be incompletely removed. Moreover, in this case, the amount of impurities entangled in the support bars is gradually increased, and gaps between the screen bars adjacent to the support bars are slowly clogged with impurities entwined around the support bars. Ultimately, most of the gaps are clogged with impurities, thus inducing the overflow of wastewater.